The present invention relates to a method and apparatus for controlling the flow of a temperature regulating fluid through a supply conduit to one or more thermal loads. In particular, the apparatus is concerned with a closed loop control for regulating the flow of a heat transfer fluid by means of a sensor that measures the cooling or heating capacity of a sampled portion of the fluid in a flow path parallel to the thermal loads.
Temperature control systems, especially those for aircraft and other systems that may include radar, avionics and other sensitive electronic equipment, are generally automatically controlled in accordance with the various limitations that are established by the craft and the system in which the controls are installed. In general the control systems employ a temperature sensor which produces a signal that is applied to a flow modulating device to control the volume or flow rate of a temperature controlling fluid, such as air, through the avionics and other compartments or fixtures which represent thermal loads to the temperature control system.
In power dissipating units such as avionics and other electronic compartments excessive heat is generally produced and, accordingly, cooling is required to maintain the temperature of the electronic components within a predetermined temperature range. However, other components which are positioned in particularly cold locations in a craft may require heating and, accordingly, it should be understood that within the scope of the present invention reference to a temperature regulating or heat exchange fluid is intended to apply to fluids which either heat or cool a thermal load.
One type of prior art temperature control system utilizes a cooling effect sensor which measures the cooling capacity of a fluid that is supplied to a thermal load. In such a sensor, a portion of the heat transfer fluid is sampled in a conduit that extends in parallel relationship with the thermal load, and a heater which effectively simulates a thermal load applies heat to the sampled fluid at a regulated rate. The heater is generally an electrical heater supplied with current at a regulated voltage and the temperature sensor is integrally mounted on a layer of insulation surrounding the heater. In operation the sampled fluid flows over the heater and removes heat in a manner dependent upon the cooling capacity of the fluid, and the heater temperature measured by the sensor reflects that capacity.
It is an object of the present invention to provide a closed loop temperature control system utilizing an improved sensor to detect the cooling or heating capacity of a fluid and to modulate the flow of the fluid through a thermal load accordingly.